Mercury vapor glow lamp



y 1940. J. w. MARDEN ET AL I 2,199,956

MERCURY VAPOR GLOW LAMP Filed March 21, 1930 INVENTORS Patented May 1, 1940 PATENT OFFICE MERCURY VAPOR GLOW LAMP John W. Marden, East Orange, and Madison G. Nicholson, In, South Orange, N. J., assignors, by mesne assignments, to Westinghouse Electric and Manufacturing Company, East Pittsburgh. Pa., a corporation of Pennsylvania Application March 21, 1930, Serial No. 437,659

Claims.

This invention relates to a lamp for the production of ultra violet radiations and more particularly to a gaseous conduction lamp of the negative glow type which yields a spectrum relatively rich in ultra violet light.

Ultra violet light has long been recognized as beneficial in therapy but heretofore the greater number of available sources of artificial ultra violet light have been are devices, such as carbon,

iron, mercury vapor or tungsten arcs all of which v require comparatively high operating current which are difficult to control, usually requiring expensive auxiliary equipment and the general application of such devices has been somewhat restricted, particularly with respect to use in living rooms where a mild source of ultra violet radiation is desirable.

One of. the primary purposes of the invention is to provide rooms, such as living rooms of dwellings with a sufficient amount of ultra violet light to give as near as possible the equal of natural sunlight conditions and to so construct the ultra violet producing device that it may be readily inserted into the ordinary lighting socket as for example, on lines of 110 to 220 volts and further to combine a source of ultra violet radiations with a source of artificial illumination so as to provide a unit which serves the dual function of providing illumination and ultra violet light and in utilizing the light source as an operative part of the source of. ultra violet light.

One of the objects of the present invention therefore is to provide a source of ultra violet light suitable for household or layman application which may be operated from 110 or 220 volt alternating light source without auxiliary equipment and which requires no more attention than is necessary in connection with the ordinary incandescent filament lamp.

Another, object of the invention is to provide a lamp which will give a mild form of ultra violet radiation in an economical manner from an operating standpoint and which is of simple construction and of relatively low cost.

Other objects and advantages of the invention will manifest themselves from the following description. I

In accordance with the present invention a lamp is produced to give a mercury glow with a consequent emanation of ultra violet light at relatively low current.

Attempts have heretofore been made to 'produce gaseous conduction lamps for operation on commercial line voltages but the disadvantages presented such as overheating in the absence of expensive equipment for regulation, arcing, blackening and what is termed sputtering, made such lamps as heretofore constructed, impractical.

It has been discovered that a gaseous conductionlamp which avoids the above disadvantages may be produced by employing one or more indirectly heated cathodes preferably two cathodes for operating on A. C. circuits each of which is comprised of a coiled filament surrounded by a metallic sleeve having thereon a coating of thermionically active material.

The filaments of the cathode assemblies are connected in series and in predetermined space relation within an actuated envelope containing mercury vapor. The heater elements of the cathodes may be so proportioned as to give a desired voltage drop.

The above described cathode which may be termed a cathode assembly is somewhat similar to that employed in radio tubes of the indirectly heated cathode type and as above mentioned it has been found that a cathode assembly of this character makes it possible to produce a gaseous discharge device yielding ultra violetlight.

The new use to which the cathode assembly is put, however, makes it essential to change the construction and operation thereof to meet the conditions attending a glow discharge lamp. For example, whereas in the cathode assembly as used in an audion it is essential to provide a cathode surface which is electrically distinct from the heater element, the present invention requires a construction wherein the heater element is electrically connected with the cathode surface.

With this arrangement of the component parts of the cathode assembly a device is produced which is self-regulating. For example when a glow lamp constructed in accordance with the present invention is in operation the lower the voltage drop between the terminals the lower the current fiow in the heater elements or filaments so that when the emission of the cathode surface is high the glow is large and the filament heating current is small.

If the temperature of the cathode drops, electron emission also drops and the glow current becomes less, raising the voltage across the terminals so that the heating current'is increased and the temperature of the cathode raised to a point where the electron emission causes a reduction in the amount of current passing through the filament and thus limits the temperature of the cathode.

In addition to the, self regulating feature attending the use of a cathode assembly of the above character it has been found that the same aids in producing a glow discharge in the absence of sputtering since by reason of the indirect heating of the cathode there is no variation in potential along its length and a so called umpotential surface is provided and a uniformity in the degree of discharge prevails.

A glow lamp constructed in accordance with the present invention may be operated at line voltage when placed in series with a suitable resistance. Inasmuch as the present device provides a mild form of ultra violet light and is of advantage for use in living rooms where it is desired to provide ultra violet radiations to approach the beneficial results attained by sunlight, it is desirable to operate the present lamp in series with an incandescent electric lamp which will serve for illuminating purposes.

From the above it will be evident that the device is self regulating to keep the voltage drop across the glow tube relatively constant and to regulate the temperature of the cathode. By reason of the self regulating feature it is possible to use a lamp constructed in accordance with the present invention under a variety of conditions. For example, two glow lamps may be used in series with a 75, 100 or 150 watt lamp as will be hereinafter more fully described.

A combination of the three lamps above mentioned makes it unnecessary to use auxiliary equipment such as transformers and the three lamps may be connected in the ordinary lighting circuit by means of a triple socket arranged to connect the lamps in series. Where the lamps are to operate on 110 volts the glow lamps may be operable at 15 to 20 volts and the incandescent lamp at 80 volts although an ordinary 100, 150 or 200 watt 110 voltlamp may be used.

When using a triple lamp combination as above set forth it has been found that about 80 volts are used for illumination and 40 volts in the glow lamps.

Although a great variety of combinations and arrangements may be employed the invention is shown in Fig. 1 of the drawing as employing a three way socket for connecting two glow lamps and one incandescent lamp in series.

Fig. 2 shows a vertical sectional view of one of the cathode assemblies of a glow lamp.

Fig. 3 is an enlarged view taken on line III- III in Fig. 2.

Fig. 4 is an enlarged view taken on line IV-IV in Fig. 2, and

Fig. 5 is a fragmentary view of a bulb havi one cathode assembly and an anode.

Although the present invention is applicable to a variety of combinations with one or more glow lamps it is shown as embodying two glow lamps I and II and an incandescent electric lamp l2 all of which are connected in series with a source of potential indicated at 13.

The incandescent lamp may be of the usual type comprising a bulb H of a glass transparent to ultra violet light if desirable and having a mount l to support afilament l6 constructed and. proportioned for 80 volts. The lamp may have the customary screw base I! for entrance into a socket I 8 of a three way socket unit l9, indicated in dotted lines. The unit l9 may be provided with the usual screw plug 2| connected with conductors 22 and 23 from the power source l3.

The glow lamps l0 and II are of similar construction and a description of one will answer the carbonates of the alkali earth metals.

for both. Considering lamp III the same may comprise a bulb 24. The bulb 24 may be of any suitable glass transparent to ultra violet light, good results having been obtained when usi what is known as a Corex D bulb having a neck aperture with an inside diameter of about 39 millimeters to admit the mount. A mount 25 may be sealed in the bulb after which a few cubic millimeters of mercury 26 may be poured into the bulb through the exhaust tube 21. Satisfactory results have been obtained by adding mercury sufficient to give the bulb from one tothree cubic millimeters of mercury after sealing off. Before sealing off, however, the bulb, while on the vacuum pump may be baked for five minutes at 400 C. The coating material on the cathodes is decomposed for three minutes with a standard 150 watt lamp in series with the glow lamp on a 115 volt A. C. line and then seasoned for two minutes while in series with a 200 watt lamp.

The bulb is then sealed or tipped oif at 28 in the usual manner. A screw base 29 may then be secured to the bulb by cement 3| making the lamp ready to be inserted into a socket 32 of the unit I9.

In the glow, lamp shown which is operable on alternating current the internal structure or mount 25 consists of the usual stem tube 33 having lead wires 34 and 35 embedded in a press portion 36.

The lower end of lead wire 34 is connected to a bottom contact 31 of the base 29, this contact being insulated from the metallic shell of the base. The lower end of the lead wire 35 is con nected at 38 with the metallic shell of the base so that when the base is disposed in a socket a conductor 39 may connect with the conductor 23 and a conductor 4| may connect with a side contact 42 of the lamp l2. The side contact 45 of the glow lamp H may be connected by means of a conductor 44 with the bottom contact 43of the lamp l2. The bottom contact 46 of the glow lamp is connected by conductor 41 with conductor 22 through a bottom contact 48 on the screw plug 2|. It will be evident that the several lamps will be connected in series and receive electrical energy from the source 13.

Referring now to the internal structure of the glow lamps as for example lamp I 0, it willbe noted that the same contains two cathode assemblies 5| and 52 supported between ends of lead wires 34 and 35 and a cross piece 53 secured to an arbor 54 extending upwardly from the press 36.

Each cathode assemblyas more clearly shown in Figs. 2 to 4 includes a coiled filament 55. When constructed to provide a lamp having a drop of about 15 volts the filament 55 consists of a nonsag tungsten space wound coil, wound on a 21 mil mandrel with about 125 turns per inch. The wire may be of a weight of from 21 to 22% milligrams. Each filament may consist of a 15 mm. coil length including about '75 turns of wire wound as above described.

The lead wires 34 and 35 may be 25 mil nickel wire. Surrounding the filament is tubular metallic sleeve 56 having thereon a coating 51 of electron emission material which may be any suitable material. For example the surface of the sleeve may be coated with a quick drying binder such as nitrocellulose in amyl acetate, with The carbonates are stable in atmosphere and may be stored for indefinite periods without detrimental effects. After the cathode assembly has been completed and mounted within the evacuated envelope or'bulb, the-carbonate coating is converted to the oxides ofthe alkaline earth metals by heating the cathode to a sufficiently high temperature as above described. The filament l! as shown, is supported with its longitudinal axis coincident with the longitudinal axis of the sleeve .56 by securing opposite ends or terminals of the of the cathode assembly and provide a chamber 63 for confining the heat radiated from thefilament il'to'more effectively produce thermal electron emission from the coating 51 during an operation of thedevice.

The sleeve 65 of each cathode assembly is electrically connectedwith a lead wire as for example lead 35 (Fig. 2) by a conductor 60' having one end welded or otherwise secured to the sleeve and the opposite end secured to the said leadwire. v I

Although the above described form of cathode assembly wherein end plugs are employed in the absence of an insulating wall is preferable, it is evident that if desired a cathode assembly may be employed wherein the filament is enclosed in an insulating material having an outer sleeve exteriorly coated with an electron emission material. It is obvious that the cathode assembly may ,vary as to its dimensions but goodresults have been obtained by the use of a filament of the' above given proportions when used with a nickel sleeve of about 1 to 2 mil thickness, 120 mil outside diameter and about I'l mm. inv length having the electron emission material covering cathode assemblies is not very critical and considerable'latitude may be allowedas to spacing.

In operation the current may becaused to flow and pass through the filaments or heater elements 55 which elements are surrounded by the sleeve 56 having the exterior coating of thermionically active material 51. The heat radiated from the heater-elements elevates the temperature of the material 51 to a point where electron emission occurs. The lamp l2 simply serves as a ballast to regulate the amount of current taken from'the lighting circuit or source l3.

A glow lamp may be provided for use on D. C. lines by providing a structure as shown in Fig. 5 in which a cathode assembly is disposed in proper space relation to a plate or anode 66. The structure of the cathode assembly is obviously the same as shown in Fig. 1 and may be supported at one end of a cross piece 61, the opposite end of the cross piece being secured to the plate 88. The leads and other electrical connections being the same since the plate 66 is in the same position as one of the filaments when two cathode assemblies are employed.

When electron emission starts the mercury vapor is ionized giving a glow and producing ultra violet light. Current flows between the cathodes which are alternately negative and positive with vrespect to each other.

sion to permit a glow current. I t

The cathode surfaces 51 are electrically connected tothe lower filament or heater element lead-wires 34 and 35 so that the flow of glow current does not "pass through the heater elements.

As above mentioned when the heater elements raise the temperature of the cathode surfaces to an electron emitting temperature, the glow discharge starts and the voltage drop across the heater element leads thereby decreases and less of electronic and ionic current flows through the heater elements, thus lowering the temperature of the heater elements to such'a point as to maintain the cathode surfaces at a temperature at which electron emisv sion is sufficient, but not in excess. For example, if the line voltage increases therebyincreasing the current, the cathode being still at the previous temperature has not the necessary emission to carry the added current thus the added current fiows through the heater elements and raises the temperature of the cathode surfaces until emission is sufilcient to produce a uniform operating equilibrium. i

The present invention therefore provides a self regulating glow discharge tube and when a balance is established the temperature of the oathodes remains quite'constant and maintain a continuous glow without being eflected by fluctuation of line voltages, small changes in the ballast lamp,

etc. By reason of the self regulating action of the present device it is possible to operate within relatively wide limits without overheating and spoiling the cathodes.

When the lamp is in operation the glow fills the entire bulb in the absence of a concentrated are between small points as is the case in certain other types of lamps employed for the production of ultra-violet light. Furthermore the present glow lamp operates to the extent of its capacity a few seconds after the current is turned on whereas lamps as heretofore constructed usually take about five minutes before the ultraviolet light becomes constant.

The present invention provides a device of simple construction and of relatively low cost for providing a source of ultra violet radiations and the possibility of detrimental effects from use as for example burning or over dosing is extremely small particularly if the lamp is used without a focusing reflector.

Owing to the novel construction employed, glow lamps made in accordance with the present invention have a relatively long life and have been burned 600 hours without failing.

Although specific dimensions have been given herein as an example of a selected embodiment of the invention it is obvious that the device may be made in various sizes. For example a 10 watt or a 40 watt glow lamp may be made, more: over, a considerable variation in the amount of ultra violet radiations maybe obtained by increasing or decreasing the size of the ballast lamp or it may be desirable to change the dimensions of the cathode assembly.

The lamp above described has an initial drop of about 30 volts across the leads. After a few seconds burning the voltage drops and becomes constant at about volts. When using a three way combination of two glow lamps and one incandescent electric ballast lamp of 150 watt, I5 volt filament the lamp takes up a little more than one ampere of current at starting and about 1% amperes-when the glow starts.

The following is given as an example of the amount of ultra-violet intensity with different ballast lamps.

As a modification or the present combination of incandescent electric lamp and glow lamp a composite lamp may be made comprising a bulb having two compartments, one of which may be exhausted and without mercury vapor and contain the ballast filament, while the other may have the cathodes in an environment of mercury vapor.

Although a preferred embodiment of the invention is set forth and described herein it is to be understood that modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. In an electric discharge lamp, an envelope containing an ionizable gas, two spaced apart resistance heater elements within said envelope, a pair of thermionically active electrodes each of which comprises a tubular member surrounding one of said heater elements and adapted to be heated by the latter and closed at both ends by insulating means, a lead-in wire for each electrode, one of the ends of each of said heater elements being connected to' their respective electrodes through the insulating means at one of the ends of said electrodes, and means for connecting the other ends of the heater elements through the insulating means at the other ends of said electrodes.

2. In a discharge system, the combination or a gaseous discharge tube having an envelope containing an ionizable gas and provided with a pair of resistance heaters therein, a pair of thermionically active electrodes each of which comprises a tubular member surrounding one of said heaters adapted to be heated by the latter and closed at both ends by insulating means, a main discharge circuit, a heater circuit, the current required by the resistance heaters being small relative to the current required for the main discharge between said electrodes, and an impedance common to both said circuits and in series therewith in their connection to an electrical supply source whereby the energy supplied to the heater circuit is reduced when the main discharge is established.

3. In agaseous discharge system, a discharge 1. tube having an envelope containing an ionizable gas and provided with two spaced apart resistance heaters within said envelope connected in series and adapted for a voltage higher than the ionization potential of said gas, a pair of thermionically active electrodes each of which comprises a tubular member surrounding one of said heaters and adapted ,to be heated by the latter and closed at both ends by insulating means, the main discharge path being connected in shunt to Y the heaters, and an impedance in the connection of the main discharge path to the supply line whereby upon starting of the main discharge the heating eflect or, the heaters on the main -elec-,,-

trode is materially reduced.

4. A gaseous discharge device comprising an enclosing envelope having an ionizable medium therein, a plurality of spaced apart electrodes within said envelope, a heater for each of said electrodes, said electrodes comprising a tubular member surrounding said heater andadaptedto be heated by the latter and closed at both ends a by insulating means, an electrical connection between each heater and its respective electrode, each of said heaters having a lead-in conductor connected to one end thereof and extending through the insulating means at one of the ends of said electrode and through the wall or the envelope, the other ends of the heaters being electrically connected within'the envelope through the insulating means at theflother ends oi. said electrodes, and an impedance in series with said electrodes whereby the electrical energy supplied to the heaters is reduced when a discharge occurs between said electrodes.

5. A gaseous dischargedevice comprising an f enclosing envelope having an ionizable medium therein, a plurality of spaced apart electrodes within said envelope, a common support for said electrodes, a heater for each electrode, said electrodes comprising a tubular member surrounding each heater and adapted to be heated by the lat-,

the envelope and through the-insulating meansat the other ends of said electrodes, and an impedancein series with said electrodes whereby the electrical energy supplied to the heaters is reduced when a discharge occurs between said electrodes.

JOHN W. MARDEN. I MADISON G. NICHOLSON, JR. 

